But has gas mileage really improved over the past 30 years, and what do automakers really need to do in order to ensure their cars meet tough new Corporate Average Fuel Economy targets by 2025?

According to MIT economist Christopher Knittel, the answer is simple: maintain the same rate of automotive technological innovation we’ve seen since 1980s while simultaneously replicating the average weight and power of new cars sold 30 years ago.

Has Gas Mileage Changed?

Thirty years ago, the U.S. was recovering from the second major oil crisis to hit the nation.

With gas prices still high, high gas mileage cars like the 1982 Volkswagen Rabbit proved a popular choice for those wanting to save as much at the pump as possible, while older cars like the original 1973 Honda Civic offered used car buyers a way to avoid high fuel bills.

Both of these examples, along with many other older cars, are capable of producing gas mileage rivaling or even beating modern-day fuel sippers like the 2012 Chevrolet Sonic.

In fact, if you look at the change in gas mileage between a car made in 2006 and 1980, there’s an average fuel economy increase of just 15 percent, while average curb weights have increased by 26 percent, and power by a massive 107 percent.

Larger, Faster, Safer

Why the disparity between power and weight increases and fuel economy?

It’s simple. Cars have got a whole lot more complex. Thirty years ago, satellite navigation systems and complex entertainment systems were unheard of. And electric windows, crumple zones and airbags were considered high ticket items on luxury cars like the 1981 Mercedes-Benz S-Class.

As more safety and entertainment features are added to a car, so the weight increases. In order to compensate, automakers have had to increase engine power.

What we’ve been left with, Knittel explains, are larger, faster, safer cars whose engines are actually 60 percent more efficient than engines produced 30 years ago. But because modern day cars are so much heavier and require more energy to move, any gas mileage improvements in engine design are not as great as they could be.

The Solutions

Although Knittel praises developments in fuel injection technology, engine control systems, lighter engine components and variable-speed transmissions his report, he also concludes that making cars smaller and less powerful is the key to better fuel economy.

According to his own calculations, Knittel says automakers have already built engines that are technically capable of meeting 2025 CAFE standards, but need to reduce both the curb weight and power output of the average vehicle by 25 percent in order to transfer that gas mileage from the laboratory and onto the road.

In other words, Knittel wants cars to go on a diet, or go back to the same weight and power output they had in the 1980s.

Incorrectly applied though, bad policy could make matters worse. “If you force people to buy more fuel-efficient cars through CAFE standards, you actually get what’s called ‘rebount’, and they rive more than they would have,” he cautioned.

The Reality

Thanks to developments in carbon-composite technologies, automakers have already started to make cars lighter. But a 25 percent drop in curb weight is a big challenge, especially if current safety and entertainment levels are to be kept.

And power? Academically, Knittel’s research makes sense, but we’re not sure the average car buyer is ready to give up the extra horsepower we’ve all become so used to.

We think a better solution lies in the world of plug-in vehicles, combining small gasoline engines with efficient electric motors to increase gas mileage and reduce emissions, but what do you think?